The long-term goal of this proposal is to understand the dynamics of phospholipid-protein-metal ion interations and relate them to membrane functions. We propose to use a variety of physical and chemical techniques that will permit us to study the effects of various proteins and metal ions on the lateral organization of lipid bilayers, and also the manner by which various lipids can control membrane protein function. Specifically, we plan to study the role of phase separations and lipid domain structure on the function of a membrane enzyme, namely the (Na plus K)ATPase, and the role of Ca2 ion and various proteins on the mechanism of membrane fusion. In parallel to these functional studies we plan to investigate structural aspects of the interaction of several well-characterized membrane proteins with phopholipid membranes of defined composition and properties. Our approach is a synthetic one, based on the re-constitution of purified components, thus enabling us to study at the molecular level, structure-function relationships not otherwise amenable to detailed investigation. Our methodology combines biochemical techniques such as purification, organic synthesis and enzymatic characterization, with biophysical techniques such as differential scanning calorimetry, batch microcalorimetry, x-ray diffraction, fluorescence polarization, isopiezic monolayer expansion, ion transport, freeze-fracture electron microscopy.